In many applications, such as on board ships, there is a need for a light-weight, reliable portable engine-pump unit. For example, such units are used as portable fire fighting pumps or dewatering pumps. Present-day engine-pump units of the indicated type generally utilize a two-stroke gasoline engine because this engine is light in weight. However, the use of a fuel such as gasoline involves inherent safety problems because of the dangerous nature of gasoline which is highly flammable.
A rotary piston engine (Wankel engine) is ideal for units of the indicated type because of its light weight, its compactness, and its high speed characteristics. Also, this engine would be safer because its combustion characteristics permit it to be run on diesel-type (low volatile) fuels easier than a two-stroke gasoline engine. However, this use has not occurred because of the difficulty in starting an engine with a diesel-type fuel.
It is the general object of this invention to provide a safe fuel supply means for a portable engine-pump unit of the indicated type. The fuel supply means of the invention eliminates the need for gasoline as a fuel supply on board ships for the purpose of running portable engine-pump units of the indicated type.
In accordance with the invention there is provided a engine-pump unit that utilizes a rotary piston engine (Wankel engine) which is provided with a dual fuel supply comprising means for supplying a running fuel of relatively low volatility for use in the normal operation of the rotary engine and means for supplying a starting fuel of high volatility for use in starting the rotary engine.
In accordance with a more specific feature of the invention the starting fuel supply means comprises a sealed pressurized cartridge containing a supply of the starting fuel. The cartridge is relatively small, structurally strong and explosion-proof. The starting fuel is preferably propane which may be connected directly to the induction pipe of the carburetor system.
In accordance with a more specific aspect of the invention there is provided means cooperable with discharge passage of the cartridge for opening the same to release the contained pressurized starting fuel, and a lever means for causing a penetrating mechanism to extend within the discharge passage of the cartridge for opening the same.
In accordance with a still further aspect of the invention there is provided means responsive to the movement of the lever means to open the cartridge for causing the engine starter switch to energize the starter means for the rotary engine.
It will be apparent that the fuel supply means of the invention obviates the need for the use of gasoline as a fuel supply for an engine-pump unit on board ship. Thus, the running fuel may comprise a suitable diesel-type fuel of low volatility and the starting fuel is contained in a safe storage arrangement by the use of the cartridges. The use of the cartridge supply arrangement obviates the need for any bulk storage of a dangerous fuel on board the ship.
In accordance with a further feature of the invention there is provided a small air pump that can be used to pressurize the running fuel supply means so as to provide a simple fuel injection system.
In accordance with another aspect of the invention there is provided means for raising the temperature of the diesel-type fuel supplied to the engine so as to improve the combustion efficiency of the rotary piston engine. In a typical reciprocating piston diesel engine air is drawn into the cylinder and is compressed to a very high ratio of about 14:1 to 25:1. This high compression causes the air in the cylinder to be heated to a temperature of 700.degree.-900.degree. C. This high temperature causes spontaneous ignition of the diesel fuel that is injected into the cylinder. On the other hand, a rotary piston engine only has a combustion ratio of about 7:1 thereby providing a temperature rise in the combustion chamber of only about half that of the typical diesel engine. Accordingly, there are problems in both starting and running a rotary piston engine with a diesel-type fuel. In accordance with the invention there is provided various means for obviating this problem by raising the temperature of the diesel-type fuel so as to increase the combustability thereof and thereby improve the running and starting performance of a rotary piston engine using diesel-type fuel.
One form of fuel heating means in accordance with the invention comprises an electric resistance heater for the fuel contained in the carburetor fuel bowl. This heater is energized from the engine starter battery and there is preferably provided a thermoswitch means to control the heating action so as to maintain a desired temperature of the fuel in the fuel bowl.
Other fuel heating means in accordance with the invention involve an electric resistance heater immersed in the fuel tank, a heating jacket for heating the fuel passing through the fuel line, which jacket can be mounted on the engine exhaust, and exothermic pellets that can be added to the fuel tank for heating the same by means of an exothermic reaction resulting from the dissolving of these pellets.
All of the above-described fuel heating means are thermally insulated where possible to prevent heat loss at their heating location.